1. Field of the Invention
This invention relates to an image heating apparatus suitable for being mounted as a fixing apparatus in a copying machine or a printer, and particularly to an image heating apparatus having a flexible sleeve.
This apparatus can be used as an image heating and fixing apparatus in an image forming apparatus such as an electrophotographic copying machine, a printer or a facsimile apparatus, i.e., an image heating and fixing apparatus for heating and fixing a toner image formed on transferring paper (such as a transferring material sheet, an electrofax sheet, an electrostatic recording sheet or printing paper) as a permanently secured image by suitable image forming process means such as electrophotography, electrostatic recording or magnetic recording by the use of a toner composed of heat-soluble resin or the like.
Also, this apparatus can be used, for example, as an apparatus for heating transferring paper bearing an image thereon and improving the surface property thereof (lustering or the like), or an apparatus for tentatively fixing an image.
2. Description of Related Art
The image heating apparatus having a flexible sleeve as described above is proposed, for example, in Japanese Patent Application Laid-Open No. 63-313182, Japanese Patent Application Laid-Open No. H2-157878, Japanese Patent Application Laid-Open No. H4-44075, Japanese Patent Application Laid-Open No. H4-204980, etc., and in contrast with other known heating apparatuses or image heating and fixing apparatuses of a heat roller type, a hot plate type, a belt heating type, a flash heating type, an open heating type, etc., it has advantages that i), it can use a low heat capacity linear heating member as a heating member, and thin film of low heat-capacity as film and therefore, the saving of electric power and the shortening of wait time (improvement in quick starting property) become possible and the temperature rise in the interior of the apparatus can be suppressed, that ii) in the image heating and fixing apparatus, a fixing point and a separating point can be set discretely and therefore offset can be prevented, and that various disadvantages peculiar to apparatuses of the other types can be solved, and is an effective apparatus.
FIG. 8 of the accompanying drawings is a side cross-sectional model view of an example (an image heating apparatus) of an image heating apparatus having a flexible sleeve (film), and FIG. 9 of the accompanying drawings is a front cross-sectional model view of the heating apparatus. FIG. 10 of the accompanying drawings is a downward perspective model view of a film guide member 10 which will be described later.
The apparatus of this example is a heating apparatus of a so-called tensionless type film heating type disclosed in Japanese Patent Application Laid-Open Nos. H4-44075 to 44083, Japanese Patent Application Laid-Open Nos. H2-204980 to 204984, etc., and is an apparatus which uses cylindrical endless film as heat-resistant film and in which at least a portion of the circumferential length of this film is always made tension-free (a state not subjected to tension), and the film is adapted to be rotatively driven by the rotative driving force of a pressure roller.
The reference numeral 100 designates a holder for adiabatically supporting a heating member 3, and it also serves as a guide member for the inner surface of the film (hereinafter referred to as the film guide).
The heating member 3 is a linear heating member of low heat capacity long sideways, and is fixedly supported by being fitted into and adhesively secured to a groove 100a formed in the outer lower surface of the film guide 100 along the length thereof.
The heating member 3 quickly rises in temperature by an electrical energization heat generating resistance member 4 generating heat over the full length thereof by the electrical energization of this electrical energization heat generating resistance member 4, and the temperature rise is detected by a temperature detecting element 6 and is fed back to a control system, not shown, and the electrical energization of the heat generating resistance member 4 is controlled so that the temperature of the temperature detecting element 6 may be maintained at a predetermined set temperature during image heating.
The reference numeral 2 denotes cylindrical heat-resistant film fitted on the film guide 100 holding the heating member 3, and it is loosely fitted on the film guide 100 with a surplus of the circumferential length thereof.
The reference numerical 70 designates regulating members disposed as film draw movement regulating means on the left and right end portions of the film guide 100 for receiving the end portions of the film.
The reference numeral 8 denotes a pressure roller for forming a pressure contact nip portion (fixing nip portion) N with the film 2 interposed between it and the heating member 3, and rotatively driving the film 2, and it has a metal shaft 8a and a heat resisting rubber layer 8b of silicon rubber or the like good in mold releasing ability. A metallic stay 15 is provided on the film guide 100, and pressure springs 13 are disposed between an apparatus frame 12 and the stay 15 to thereby apply predetermined pressure to the nip portion N.
A rotative driving force is transmitted to the pressure roller by driving means M through a motive power transmitting system, not shown, whereby the pressure roller is rotatively driven in a counter-clockwise direction indicated by arrow.
A rotating force acts on the film 2 by the frictional force between the pressure roller and the outer surface of the film by the rotative driving of the pressure roller 8 (when a material P to be heated is introduced into the pressure contact nip portion N, a rotating force indirectly acts on the film 2 through the material P to be heated), and the film 2 is rotatively driven in a clockwise direction a indicated by arrow while sliding in pressure contact with the surface of the heating member 3. The film guide 100 facilitates the rotation of this film 2.
On the basis of a print command signal or on the basis of a signal when the leading edge of the material P to be heated bearing thereon an unfixed visible image (toner image) to be fixed is detected by a sensor (not shown) disposed on this side of the apparatus, the rotative driving of the pressure roller 8 is started and the temperature rise of the heating member 3 is started.
In a state in which the rotating peripheral speed of the film 2 by the rotation of the pressure roller 8 has become steady and the temperature of the heating member 3 has risen to a predetermined level, a recording material P as the material to be heated having thereof an image to be fixed is introduced into between the film 2 and the pressure roller 8 in the fixing nip portion N and is nipped and transported through the fixing nip portion N with the film 2, whereby the heat of the heating member 3 is imparted to the recording material P through the film 2 and the unfixed visible image T on the recording material P is heated and fixed on the surface of the recording material P. The recording material P passed through the fixing nip portion N is separated from the surface of the film 2 and is transported.
In the apparatus of such a tensionless type film heating type, during the rotatively driven state of the film, tension acts only the fixing nip portion N and a contact portion area between the outer surface portion of the film guide upstream of the fixing nip portion N with respect to the direction of rotation of the film and the film, and tension does not act on the most of the remaining portion of the film.
Therefore, the draw moving force of the film 2 along the length of the film guide during the rotatively driven state of the film is small, and the film draw movement regulating means or film draw controlling means can be simplified. For example, the film draw movement regulating means can be made into a simple one like a regulating member 70 having a flange 70a for receiving an end portion of the film, and the film draw controlling means can be omitted to thereby achieve a reduction in the cost and downsizing of the apparatus.
As shown in FIG. 10, a plurality of ribs 110 are provided on the film guide 100 to thereby reduce the area of contact between the film 2 and the film guide 100, thereby decreasing the frictional resistance between the film 2 and the film guide 100, and stabilizing the rotational movement of the film 2.
However, the above-described conventional image heating apparatus having a flexible sleeve has suffered from problems shown below.
The ribs 110 of the film guide 100 stably regulate the rotational moving shape of the film, but if the ribs strongly contact with the film 2, stress is applied to the film in that portion and therefore, there is the possibility of the traces of the ribs uniformly remaining in the circumferential direction of the film, and in the worst case, the film was broken in those portions.
FIG. 6 of the accompanying drawings is a view of the film guide 100 as it is seen from the fixing nip surface side.
As shown in FIG. 6, the ribs 110 are disposed are downstream of the film guide 100 relative to the fixing nip portion with respect to the transport direction of the material to be heated, but during the rotational movement of the film, the film is rotated from an upstream-to-downstream direction and therefore, the film becomes rather tensioned relative to the ribs on the upstream side of the nip portion and becomes rather loosened relative to the ribs on the downstream side of the nip portion. Accordingly, in almost all cases, it is the ribs on the upstream side that injures the film.
Such a phenomenon occurs particularly remarkably in a case where the shapes (contours) of the sliding surfaces 70b of the regulating members 70 for regulating the rotatively moving shape of the film relative to the inner surface of the film and the sliding surfaces 10b of the ribs 110 relative to the inner surface of the film differ from each other and the contour of the ribs 110 is not inside the contour of the sliding surfaces 70b of the regulating members 70, but assumes a shape jutting out to upstream of the contour of the sliding surfaces 70b of the regulating member 70.
FIG. 7 of the accompanying drawings shows such a state, and is a cross-sectional view showing construction in which the film 2 and the regulating members 70 are combined with the film guide 100 as it is seen from the fixing nip surface side.
If as shown in FIG. 7, the sliding surfaces of the ribs 110 relative to the inner surface of the film jut out to upstream of the sliding surfaces 70b of the regulating members 70 relative to the inner surface of the film, the end portions of the film are regulated to downstream of the ribs by the sliding surfaces 70b of the regulating members 70 and therefore, the film becomes very strongly tensioned between the ribs at the lengthwisely opposite ends of the film guide lying at locations nearest to the regulating members and the regulating members. If in such a state, the film is rotatively moved, the film may be injured circumferentially thereof by the frictional contact between the ribs at the opposite ends and the inner surface of the film and finally, the film may be cut at these locations.
Usually, the circumferential lengths of the sliding portions 70b of the regulating member relative to the inner surface of the film are set so as to be substantially equal to the inner circumferential length of the film with a very slight clearance so as not to be too loose relative to the inner circumferential length of the film. This is because if the circumferential lengths of the sliding portions of the regulating members relative to the inner surface of the film are extremely smaller than the inner circumferential length of the film, the movement of the film will not be stable and buckling will become liable to occur at the end portions of the film.
Thus, the rotative by moving shape of the film is regulated chiefly by the regulating members at the opposite ends, whereas the portions in which the ribs jut out more than the sliding surfaces 70b of the regulating members 70 assume a shape unnaturally jutting out as the film and are subjected to strong stress. Such a phenomenon is more liable to occur as the rotatively moving speed of the film becomes higher and a load to which the film is subjected becomes greater.
Also, if the ribs are thus in strong contact with the film, the ribs will take away the heat of the film and therefore temperature unevenness will occur on the film. That is, the temperature of the portions of the film which are in contact with the ribs will become low and this will intactly provide uneven heating during the heating of the material to be heated at the nip, and during the heating and fixing of an image, uneven luster or faulty fixing will occur at locations corresponding to the ribs.
In the conventional apparatus, the rotative moving speed of the film was relatively low and therefore, such phenomena as the injury of the film and uneven heating did not become remarkable, and in this point of view, it was necessary to take the shapes of the regulating member and the ribs into consideration.
However, in recent years, the tendency of printers, etc. carrying an image heating apparatus of the film heating type thereon toward a higher speed is remarkable and the lives of the apparatuses tend to be required to be longer. Now that the application of such a heating apparatus of the film heating type to a high-speed machine has become strongly required, the necessity of achieving the solution of the above-noted problems has been rising as an important technical task.